Optical scanning device and image forming apparatus

ABSTRACT

A coupling lens couples a beam emitted from a light source. A light deflector deflects the beam from the coupling lens at a uniform angular velocity. A line-image imaging optical system is disposed between the coupling lens and light deflector, and causes the beam to image a line image long along main scanning directions on or in the vicinity of a deflection reflective surface of the light deflector. A scanning and imaging optical system causes the beam deflected by the light deflector to image a beam spot on a medium to be scanned. In an optical housing, the light source, coupling lens, light deflector, line-image imaging optical system and scanning and imaging optical system are disposed, and contained. A plurality of holding and fixing datums are provided for holding and fixing a light-source part including the light source and coupling lens is provided in at least one of the light-source part and optical housing.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to an optical scanningdevice and an image forming apparatus used in a digital copier, a laserfacsimile machine, a laser printer, a laser plotter and so forth, and,in particular, to an optical scanning device and an image formingapparatus in which the optical scanning device can easily be adapted toa case where a cover member is mounted on an incident/exit window of acover covering a light deflector, and an optical scanning device and animage forming apparatus for which a plurality of units are used incommon among different types of devices/apparatuses.

[0003] 2. Description of the Related Art

[0004] Recently, in an optical scanning device employed as a writingsystem of an image forming apparatus such as a digital copier, a laserprinter, a laser facsimile or the like, improvement in a recording speedis demanded. In order to improve the recording speed, there is a methodof increasing a deflection speed of a light deflector such as a polygonmirror, that is, to increase a rotation speed of the polygon mirror.However, in this method, a noise generated by the light deflector, inparticular, in the case of the polygon mirror, a zipping noise generatedby edges/corners of the polygon mirror increases. Accordingly, it isnecessary to provide a measure to lower the noise.

[0005] As a measure to lower the noise, in general, a cover covering thelight deflector is used. In this case, an incident/exit window forallowing a beam to be incident on the light deflector therethrough andalso the deflected beam to exit therefrom is covered by a transparentcover such as a glass. Thereby, it is possible to prevent the noisegenerated by the light deflector from leaking externally. Further, thismeasure can also be used as a measure to prevent external dust fromadhering the light deflector.

[0006] On the other hand, an inexpensive optical scanning device inwhich the recording speed is low, and an image forming apparatusemploying such an optical scanning device have also been developed. Insuch a situation, if both an optical system aiming improvement inrecording speed and an optical system aiming reduction of costs evenwith a low recording speed are developed independently, time is requiredfor developing each of both systems, and, also, costs are required foreach thereof. In order to solve this problem, use of an optical systemhaving a common configuration is used for both systems in which atransparent cover for soundproof and dustproof is provided in theoptical scanning device for high recording speed, while the same is notprovided for the optical scanning device for low recording speed isconsidered.

[0007] However, the transparent cover having the functions of soundproofand dustproof has a refractive function. Accordingly, when thistransparent cover is used, a path of a beam is different in comparisonto a case where the same is not used. Thus, a so-called ‘floating’occurs. Thereby, it is necessary to employ different layouts ofrespective optical components between the device using the transparentcover and the device not using the same. Therefore, different opticalhousings are needed to be provided for the respective devices. However,these different optical housings need different dies for molding them.Accordingly, the costs have up for the development.

[0008] Also in an image forming apparatus such as a digital copier, alaser facsimile machine, a laser printer or a laser plotter, developmentis proceeded with such that units used inside can be used in commonamong different types of devices/apparatuses. By using units in common,it is possible not only to increase productivity so as to reduce thecosts but also to contribute to global environmental protection becauseindustrial waste can be reduced.

[0009] With regard to an optical scanning device, in many cases, ascanning lens system is used in common among different types of devices.However, according to prices and specifications of devices/apparatuses,scanning speeds may be different from each other. In an optical scanningdevice of a high scanning speed, a rotation speed of a light deflectorshould be increased. In such a case, as mentioned above, a transparentcover for sound proof is needed.

[0010] On the other hand, even using the same scanning lens system, inan optical scanning device of a low scanning speed, a rotation speed ofa light deflector should not be increased. Therefore, in such an opticalscanning device, the transparent cover for sound proof is not needed asmentioned above. However, there are cases where, also in such an opticalscanning device of a low scanning speed, the transparent cover is usedas a measure for dustproof of the light deflector.

[0011] Further, Japanese Laid-Open Patent Application No. 11-218715discloses an optical scanning device in which, when a beam from a lightsource is directed to a deflector (polygon mirror), adjustment of alight path in a main scanning direction of the beam is enabled bytranslation in a z-axis of two mirrors disposed between the light sourceand polygon mirror.

[0012] As mentioned above, in the related art, when units of an opticalscanning device are used in common among different types of the devices,a position of imaging of a beam is different according to whether or nota transparent cover for soundproof and dustproof is provided.Accordingly, it becomes not possible to precisely image from the beamonto a surface to be scanned.

SUMMARY OF THE INVENTION

[0013] An object of the present invention is to enable to use an opticalhousing in common between a case where a transparent cover member forsoundproof and dustproof is used and a case where the same is not used.

[0014] When the transparent cover member is used, because floatingoccurs due to the refractive function thereof, the imaging position isshifted according to whether or not the transparent cover member isused. Thereby, the imaging position along the sub-scanning directions isshifted at the medium to be scanned. Thereby, the image quality isdegraded. In order to solve this problem, it is necessary to change theposition of the line-image imaging optical system according to whetheror not the transparent cover member is used.

[0015] Accordingly, another object of the present invention is todispose the light-source part and line-image imaging optical system on acommon member, and thus, the light-source part and line-image imagingoptical system can be positioned simultaneously.

[0016] As the position of the light-source part and line-image imagingoptical system is thus substantially integrally changed, the distancebetween th light-source part and light deflector is changed accordingly.When the beam from the light-source part is a divergent beam or aconvergent beam, the imaging position at the medium to be scanned in themain scanning directions is changed as the distance between thelight-source part and light deflector is changed. Thereby, a problematicsituation such as increase of beam in diameter occurs due to deviationof imaging position.

[0017] Accordingly, another object of the present invention is toprovide an optical scanning device in which, even the distance betweenthe light-source part and light deflector is changed, deviation ofimaging position can be prevented.

[0018] Another object of the present invention is to reduce the numberof parts and to miniaturize the movable part by configuring the couplinglens and line-image imaging optical system into a single lens.

[0019] Another object of the present invention is to have a plurality oflight-emitting sources in the light-source part, thus to increase thenumber of scan lines, and to increase the speed of optical writingaccordingly.

[0020] Another object of the present invention is to provide an opticalscanning device and an image forming apparatus employing the opticalscanning device through which the beam can be used for precisely imagingon the surface to be scanned whether or not the transparent cover forsoundproof and dustproof is provided.

[0021] An optical scanning device according to the present inventioncomprises:

[0022] a light source;

[0023] a coupling lens coupling a beam emitted from the light source;

[0024] a light deflector deflecting the beam from the coupling lens at auniform angular velocity;

[0025] a line-image imaging optical system disposed between the couplinglens and light deflector, and causing the beam to image a line imagelong along main scanning directions on or in the vicinity of adeflection reflective surface of the light deflector;

[0026] a scanning and imaging optical system causing the beam deflectedby the light deflector to image a beam spot on a medium to be scanned;and

[0027] an optical housing in which the light source, coupling lens,light deflector, line-image imaging optical system and scanning andimaging optical system are disposed, and contained, and

[0028] wherein a plurality of holding and fixing datums for holding andfixing a light-source part comprising the light source and coupling lensare provided in at least one of the light-source part and opticalhousing.

[0029] The light deflector may be covered by a cover;

[0030] the cover may have a window for the beam to be incident on andexit from the light deflector; and

[0031] a transparent cover member may be able to be mounted on thewindow, and

[0032] wherein the holding and fixing datums are determined so that, byselectably using the holding and fixing datums, the beam deflected bythe light deflector passes through the scanning and imaging opticalsystem approximately at the same position whether or not the transparentcover member is mounted.

[0033] Thereby, because the plurality of holding and fixing datums areprovided and are selectably used according to whether or not thetransparent cover is mounted, it is possible that the configuration ofthe optical system and the configuration of the optical housing are usedin common between a machine/configuration for high-speed writing usingthe transparent cover covering the entirety of the light deflector and amachine/configuration for low-speed writing not using the transparentcover. In fact, one of the plurality of datums is used for the machinefor high-speed writing and the other thereof is used for the machine forlow-speed writing. Thereby, it is possible to cancel the influence ofthe transparent cover member. As a result, it is possible to reducecosts for development of the optical scanning device, and, also, shortena time therefor. Further, by using the housing in common, only a singledie for molding it is needed. Thereby, also costs can be effectivelyreduced.

[0034] The light-source part and line-image imaging optical system maybe disposed on a common member.

[0035] Thereby, these components can be moved integrally. Thereby, it ispossible to correct a shift of imaging position along the sub-scanningdirections occurring due to whether or not the transparent cover memberis used. Further, as the light-source part and line-image imagingoptical system are integrated, assembling work, adjustment work and soforth can be simplified.

[0036] The coupling lens and line-image imaging optical system may beformed integrally.

[0037] Thereby, the number of components/parts can be reduced, thecomponents can be reduced in size, and resources/materials can be saved.

[0038] The light-source part may include a plurality of light-emittingsources.

[0039] Thereby, it is possible to further increase the speed in opticalwriting/forming an image.

[0040] The beam emitted from the light-source part may be anapproximately parallel beam.

[0041] Thereby, it is possible to eliminate a shift of imaging positionalong the main scanning directions due to whether or not the transparentcover is used.

[0042] An optical scanning device according to another aspect of thepresent invention comprises:

[0043] a light-source unit emitting a beam;

[0044] a first imaging optical system causing the beam emitted by thelight-source unit to image at a predetermined position;

[0045] a deflector receiving the beam from the first imaging opticalsystem and performing scanning with the beam; and

[0046] a second imaging optical system causing the beam from thedeflector to image a beam spot on a surface to be scanned, and

[0047] wherein:

[0048] the light-source unit, first imaging optical system, deflectorand second imaging optical system are mounted in a box housing;

[0049] a transparent member of an approximately parallel plate isdisposed detachably so as to be located between the first imagingoptical system and deflector and between the deflector and secondimaging optical system; and

[0050] a mounting position of the second imaging optical system can bechanged according to whether or not the transparent member is used.

[0051] Thereby, when a plurality of units are used in common amongdifferent types of devices, it is possible to image a beam spot from abeam on a surface to be scanned precisely, whether or not thetransparent member for soundproof and dustproof is used.

[0052] The mounting position of the second imaging optical system alongmain scanning directions may be able to be changed according to whetheror not the transparent member is used.

[0053] Thereby, it is possible to reduce a deviation of a beam axis(optical-axis deviation) along the main scanning directions.

[0054] The mounting position of the second imaging optical system alongdirections of an optical axis thereof may be able to be changedaccording to whether or not the transparent member is used.

[0055] Thereby, it is possible to reduce a floating amount of an opticalimage along directions of beam axis.

[0056] The mounting position of the second imaging optical system alongthe main scanning directions and directions of optical axis thereof maybe able to be changed according to whether or not the transparent memberis used.

[0057] Thereby, it is possible to reduce both a deviation of beam axisalong the main scanning directions and a floating amount of an opticalimage along the directions of beam axis.

[0058] Further, the present invention can be applied toequipment/machines such as a digital copier, a laser facsimile machine,a laser printer, a laser plotter, and so forth. Then, because units usedinternally can be used in common among different types of devices asmentioned above, productivity is improved and costs can be reduced, and,also, it is possible to contribute to global environmental protectionbecause industrial waste can be reduced accordingly.

[0059] Other objects and further features of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060]FIG. 1 shows a perspective view of an optical scanning device towhich each of first, second and third embodiment of a first aspect ofthe present invention can be applied;

[0061]FIG. 2 shows a cross-sectional view of a light deflector, a coverand a transparent cover member of each of the first, second and thirdembodiment of the first aspect of the present invention;

[0062]FIG. 3 shows light paths for illustrating an amount to shift abeam coming from a light-source part according to whether or not thetransparent cover member is provided in each of the first, second andthird embodiments of the first aspect of the present invention;

[0063]FIG. 4 shows a perspective view of the light-source part in thefirst embodiment of the first aspect of the present invention;

[0064]FIG. 5 shows light paths for illustrating a shift of imagingposition along sub-scanning directions between cases where thetransparent cover member is provided or not in each of the first, secondand third embodiments of the first aspect of the present invention;

[0065]FIG. 6 shows a perspective view of the light-source part andline-image imaging optical system in the second embodiment of the firstaspect of the present invention;

[0066]FIG. 7 shows in more detail the light paths for illustrating theabove-mentioned amount to shift the beam coming from the light-sourcepart;

[0067]FIG. 8 illustrates the third embodiment of the first aspect of thepresent invention in which an incident angle of the beam coming from thelight-source part is changed according to whether or not the transparentcover member is used;

[0068]FIG. 9 shows a general plan view of an optical scanning device ineach of first, second and third embodiments of a second aspect of thepresent invention;

[0069]FIG. 10 illustrates a difference in light path of a beam between acase where an optical scanning device has a transparent member and acase where the optical scanning device does not have the transparentmember;

[0070]FIG. 11 shows a floating amount (C1′, C2′) of an optical imagealong directions of the axis of the beam and a deviation amount (C1, C2)of the axis of the beam in the case where the transparent member is usedin the optical scanning device;

[0071]FIGS. 12A and 12B show an essential part of the optical scanningdevice in the first embodiment of the second aspect of the presentinvention;

[0072]FIGS. 13A and 13B show an essential part of the optical scanningdevice in the second embodiment of the second aspect of the presentinvention;

[0073]FIGS. 14A and 14B show an essential part of the optical scanningdevice in the third embodiment of the second aspect of the presentinvention; and

[0074]FIG. 15 shows a general elevational sectional view of an imageforming apparatus in one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0075]FIG. 1 shows a perspective view of an optical scanning device ineach of first, second and third embodiments of a first aspect of thepresent invention.

[0076] As shown in the figure, the optical scanning device includes alight source 1 of a semiconductor laser, for example, and a couplinglens 2. A divergent beam emitted from the light source 1 is coupled bythe coupling lens 2, and thus, is condensed thereby. Then, the beam isshaped by an aperture 3 acting as a beam shaping part so as to have apredetermined shape in cross section. A cylindrical lens 4 acting as aline-image imaging optical system is disposed on a light path of thebeam having passed the aperture 3. Further, a light deflector 5 of apolygon mirror is disposed at a position which the beam having passedthrough the cylindrical lens 4 reaches.

[0077] The cylindrical lens 4 condenses the beam having passed throughthe aperture 3 only along sub-scanning directions. Thereby, the beam isused for imaging a line image long along main scanning directions on orin the vicinity of a deflection reflective surface of the lightdeflector 5. The light deflector 5 deflects the incident beam for apredetermined angle range at a uniform angular velocity. Thethus-deflected beam passes through a scanning and imaging optical system17, and is used for scanning a medium to be scanned 9. The medium to bescanned 9 is of a photoconductive photosensitive body. The scanning andimaging optical system 17 includes an imaging lens 6 and along-dimensional lens 7 long along the main scanning directions. Thescanning and imaging optical system 17 causes the beam deflected by thelight deflector 5 at the uniform angular velocity to image a beam spoton the medium to be scanned 9, and, also, to scan the medium to bescanned 9 at a uniform velocity. A long-dimensional mirror 8 bending alight path of the beam is disposed between the scanning and imagingoptical system 17 and medium to be scanned 9.

[0078] As shown in FIG. 1, the optical scanning device includes asynchronization detecting optical system 100. The synchronizationdetecting optical system 100 includes a mirror 10, a lens 11, and aphotoelectric device 12. The mirror 10 is disposed between theabove-mentioned imaging lens 6 and the long-dimensional lens 7, andreflects the beam in the vicinity of a deflection beginning end, towardthe lens 11 and photoelectric device 12. The photoelectric device 12detects the beam in the vicinity of the deflection beginning end, andoutputs a signal. This signal is, as well-known, used for determining awriting beginning timing as a synchronization signal.

[0079] An optical system including the above-mentioned light source 1,coupling lens 2, light deflector 5, line-image imaging optical system 4,scanning and imaging optical system 17, long-dimensional mirror 8 andsynchronization detecting optical system 100 is positioned at apredetermined position of an optical housing, not shown in the figure,and is enclosed thereby.

[0080] The configuration of the optical scanning device shown in FIG. 1is basically the same whether n the device is used for either high-speedscanning or low-speed scanning. However, when the device is used forhigh-speed scanning, the light deflector 5 (polygon mirror) is rotatedat a relatively high speed, as mentioned above. Accordingly, a zippingsound generated from the high-speed rotation thereof may be aproblematic noise, as mentioned above. In order to solve this problem,as shown in FIG. 2, the entirety of the light deflector 5 is covered bya cylindrical cover 13 for the purpose of soundproof. The cover 13 has awindow through which the beam to be incident on the light deflector 5passes and the thus-deflected beam exits from the cover 13. This windowis covered by a transparent cover member 14 when the optical scanningdevice is used for high-speed scanning. Thereby, the noise generated bythe light deflector 5 rotating at high speed is prevented from leakingexternally.

[0081] Whether or not the above-mentioned cover member 14 is used,almost all of the light deflector 5, imaging lens 6, long-dimensionallens 7 and so forth are used in common. However, as the transparentcover member 14 is disposed on the light path of the optical system, thelight path is shifted through the cover member 14 due to a phenomenoncalled ‘floating’. As a result, the positions of the beam at which thebeam passes through the imaging lens 6 and long-dimensional lens 7 arechanged by the cover member 14. Thereby, a position at which imaging ismade by the beam is shifted as if the optical system disposed betweenthe light deflector and the medium to be scanned 9 is shifted in adirection perpendicular to the optical axes of the lenses in adeflection and scanning plane. Thereby, a beam spot formed on the mediumto be scanned 9 increases in diameter, and, as a result, thus-resultingimage quality is degraded. Such a problem is pointed out in JapanesePatent No. 2550153 of the present applicant.

[0082]FIG. 3 illustrates the above-mentioned problem in detail. In FIG.3, a beam of a light path ‘a’ is directed to the light deflector 5 fromthe light source. In the case where the cover member 14 is provided onthe light path, the light path of the beam is such as that indicated bya solid line. On the other hand, in the case where the cover member 14is not provided there, the light path of the beam is such as thatindicated by a broken line. As shown in FIG. 3, in the case where thecover member 14 is provided, the beam is refracted by the cover member14 while the beam is incident on the light deflector 5 and also whilethe beam reflected by the light deflector 5 exits therefrom, asindicated by a solid line ‘c’. On the other hand, in the case where thecover member 14 is not provided, refraction of neither the incident beamnor the exiting beam occurs. As a result, the beam exits in a lightpath, as indicated a broken line ‘d’, different from the light path ‘c’in the case where the cover member 14 is provided. This state is theabove-mentioned state occurring as if the optical system between thelight deflector 5 and the medium to be scanned 9 is shifted in thedirection perpendicular to the axes of the lenses in the deflection andscanning plane, and, results in a shift of position of an imagingposition due to rotation of curvature of image surface, and, thus,results in increase in diameter of a beam spot.

[0083] In order to solve this problem, the light path of the beamincident on the cover member 14 from the light source in the case wherethe cover member 14 is not provided is shifted in a directionperpendicular to the axis of the beam in the deflection plane so thatthe light path of the thus-shifted beam after reflected by the lightdeflector 5 coincides with the light path ‘c’ of the non-shifted beamafter passing through the cover member 14, reflected by the lightdeflector 5 and again passing through the cover member 14. In FIG. 3,the amount of this shift is expressed by Δ, and the light path of theshifted beam incident on the light deflector 5 is expressed by ‘b’.Thus, by shifting the light path of the beam in the case where the covermember 14 is not provided in the direction perpendicular to the opticalaxis of the light source, the light path of the beam exiting from thelight deflector 5 is made coincidence between the case where the covermember 14 is provided and the case where the cover member 14 is notprovided. Accordingly, it is possible to prevent the imaging positionfrom being shifted between the case where the cover member 14 isprovided and the case where the cover member 14 is not provided.Thereby, it is possible to obtain a high-quality image.

[0084] In order to shift the light path of the beam coming from thelight source toward the light deflector 5 between the case where thecover member 14 is provided and the case where the cover member 14 isnot provided, a plurality of datums for holding and fixing alight-source part having the light source 1 and coupling lens 2 areprovided in the above-mentioned optical housing corresponding to thecase where the cover member 14 is provided and the case where the covermember 14 is not provided, respectively, and, an appropriate one ofthese datums is used case by case. A specific example thereof will nowbe described.

[0085]FIG. 4 illustrates this example. In FIG. 4, the light-source part15 acts as a holding member holding the light source 1 and coupling lens2. The light-source part 15 includes a plate-shaped vertical member 15 aholding the light source 1 and coupling lens 2, and a plate-shapedhorizontal member 15 b on which the bottom surface of the verticalmember 15 a is fixed. The horizontal member 15 b has four holes A1, A2,B1 and B2 each extending vertically at positions near the respectivecorners of a rectangle. On the other hand, in the above-mentionedoptical housing in which the light-source part 15 is fixed, pins a1 anda2 corresponding to the respective holes A1 and A2, and pins b1 and b2corresponding to the respective holes B1 and B2 are provided.

[0086] The pair of pins a1 and a2 and the pair of pins b1 and b2 areused as holding and fixing datums for holding and fixing thelight-source part 15, respectively. Assuming that the pair of pins a1and a2 are the holding and fixing datum for the case where theabove-mentioned cover member 14 is not provided, the other pair of pinsb1 and b2 are the holding and fixing datum for the case where the covermember 14 is provided. The pair of pins a1 and a2 and the other pair ofpins b1 and b2 are configured so that they do not interfere with oneanother so that, when one pair thereof are fitted in the correspondingholes so as to fix the light-source part 15 to the optical housing, theother pair do not interfere with it. For this purpose, for example, thepositions thereof are determined to be away from each otherappropriately, or, a recess or the like is provided for accommodatingthe other pins. Thus, by providing the plurality of holding and fixingdatums for the light-source part 15, corresponding to the case where thecover member 14 is provided and the case where the cover member 14 isnot provided, respectively, it is possible to prevent shift in imagingposition from occurring by appropriately changing the position of thelight-source part 15.

[0087] In the configuration shown in FIG. 4, the pair of pins a1 and a2and the other pair of pins b1 and b2 have been described as the holdingand fixing datums for the light-source part 15. However, it is alsopossible that the pair of holes A1 and A2 and the other pair of holes B1and B2 of the light-source part 15 are holding and fixing datums,instead. When the pair of pins a1 and a2 and the other pair of pins b1and b2 have been determined as the holding and fixing datums, thefollowing configuration is possible: That is, only one pair of holes areprovided in the light-source part 15, and, either the pair of pins a1and a2 or the pair of pins b1 and b2 are selectively fitted in this pairof holes of the light-source part 15. To the contrary, when the pair ofholes A1 and A2 and the other pair of holes B1 and B2 are used as theholding and fixing datums, the following configuration is possible: Thatis, only one pair of pins are in the optical hosing, and, either thepair of holes A1 and A2 or the pair of holes B1 and B2 selectively havethis pair of pins fitted therein. Thus, the position of the light-sourcepart 15 can be changed. Further, it is also possible that pins areprovided on the light-source part 15, and holes, in which the pins arefitted, respectively, are provided in the optical housing, instead. Anessential point is that a plurality of holding and fixing datums areprovided in at least one of the light-source part 15 and opticalhousing.

[0088] With reference to FIG. 5, shift of imaging position in asub-scanning directional section between the case where the cover member14 is provided and the case where the same is not provided will now beillustrated. In FIG. 5, a state indicated by a solid line 1 is a statein which the cover member 15 is not provided. In this state, a beam fromthe light-source part is used for imaging a line image long along themain scanning directions on or in the vicinity of the deflectionreflective surface 5 a through the line-image imaging system 4, and,then, is used for imaging a beam spot on the medium to be scanned 9through the scanning and imaging system 17 which is a combination of theimaging lens 6 and long-dimensional lens 7. In FIG. 5, a state indicatedby a broken line m is a state in which the cover member 14 is used. Inthis state, the beam having passed through the line-image imaging system4 is shifted by the refracting function (floating) of the cover member14, and, thereby, the line image on or in the vicinity of the deflectionreflective surface 9 a is shifted toward the medium to be scanned 9 by adistance Δx. Then, by an imaging lateral magnification β of the scanningand imaging system 17 along the sub-scanning directions, the imagingposition of the beam is shifted by a distance Δx′ at the medium to bescanned 9. There,

Δx′=Δx·β

[0089] Thus, in the sub-scanning directional section, in the case wherethe cover member 14 is used, in comparison to the case where the covermember 14 is not used, the imaging position is shifted by the distanceΔx′ along the directions of optical axis at the medium to be scanned 9.In order to eliminate this shift of the imaging position, it isnecessary to move the line-image imaging system by the distance Δx alongthe directions of the optical axis. At this time, by providing aconfiguration such that the light-source part can hold the line-imageimaging optical system 4, it is possible to easily deal with the casewhere the cover member 14 is used and the case where the cover member 14is not used, by shifting the light-source part and line-image imagingoptical system 4 integrally along the directions of the optical axis. Inthis case, the line-image imaging system 4 is positioned at a datumposition such that the position of the line-image imaging system 4 isoptimum with respect to the light-source part.

[0090]FIG. 6 shows a specific example of a configuration such that theline-image imaging system 4 is positioned at a datum position such thatthe position of the line-image imaging system 4 is optimum with respectto the light-source part. As shown in FIG. 6, the configuration includesa holding member 16 including a plate-shaped vertical part 16 a and aplate-shaped horizontal part 16 b integral with the vertical part 16 a.The light-source part 15 is mounted on the vertical part 16 a. Datumsupporting parts 16 c each having a shape of a quadratic prism areintegrally provided on the horizontal part 16 b. Surfaces of the datumsupporting parts 16 c face a surface of the line-image imaging system 4at both ends thereof. Further, the line-image imaging system 4 is fixedto the datum supporting parts 16 c as a result of being pressed theretoby a leaf spring or the like, not shown in the figure. Thus, theline-image imaging system 4 is disposed on the holding member 16 ontowhich the light-source part 15 is also disposed. Thereby, the line-imageimaging system 4 is positioned along the directions of the optical axisoptimally with respect to the light-source part 15. It is also possiblethat the line-image imaging system 4 is fixed to the datum supportingparts 16 c by adhesive.

[0091] Holes are formed in the horizontal part 16 b of the holdingmember 16 such that the light-source part 15 and line-image imagingsystem 4 integral with the light-source part 15 are fixed at apredetermined datum position of the optical housing. For this purpose,these holes have pins formed in the optical housing fitted therein. Thepins which are used to fit into the holes of the holding member 16 areselected, or the holes of the holding member 16 in which the specificpins of the optical housing are fitted are selected. Thereby, it ispossible to change the position of the holding member 16 along thedirections of the optical axis according to whether or not theabove-mentioned cover member 14 is used.

[0092] In the example (second embodiment of the first aspect of thepresent invention) shown in FIG. 6, a distance between the holdingmember 16 and the light deflector 5 is set so that the position of theline-image imaging optical system 4 is optimum according to whether ornot the cover member 14 is used. Accordingly, distances of the lightsource 1 and coupling lens 2 to the light-deflector 5 also changeaccording to whether or not the cover member 14 is used. Thus, thedeviation of the imaging position in the section parallel to thesub-scanning directions is corrected. However, the overall magnificationis different between the sub-scanning directions and main scanningdirections. Accordingly, when the imaging position along thesub-scanning directions is corrected, the imaging position along themain scanning directions is not corrected. Therefore, it is preferablethat the beam emitted form the coupling lens 2 is an approximatelyparallel beam such that the beam is not affected by the position of theline-image imaging system 4. Thereby, the beam incident on the scanningand imaging system 17 is kept as an approximate parallel beam along themain scanning directions, and, as a result, the position of theline-image imaging system 4 does not affect the state of imaging by thescanning and imaging system 17.

[0093] When the beam from the coupling lens 2 is a divergent beam or aconvergent beam, the distance between the natural beam condensedposition and medium to be scanned 9 differs due to the position of theline-image imaging optical system 4. Accordingly, the state of imagingby the scanning and imaging system 17 is affected thereby, the imagingstate is degraded, and image quality is degraded due to increase in thebeam diameter and so forth.

[0094] As a method of increasing the speed of optical writing and thusimage formation, there is a method in which the light-source partincludes a plurality of light sources, and, thus, is of a multi-beamtype, and, also, the rotation speed of the light deflector is increased.Thereby, it is possible to increase the mechanical output speedeffectively.

[0095] In order to deal with both the case where image formation is madeto be of high speed through employment of the multi-beam light-sourcepart and increase in the rotational speed of the light deflector, andthe case where image formation is made to be of low speed, the followingarrangement is made, for example: That is, when a low-speed outputmachine is configured, the light-source part includes a single lightsource, the light deflector is rotated so slowly that substantialzipping noise does not occur, and the above-mentioned cover member 14 isomitted. When the high-speed output machine is configured, multi-beamscanning is rendered through a plurality of light sources, the lightdeflector is rotated at high speed, and the above-mentioned transparentcover member 14 is used as a measure against zipping noise occurring dueto the high-speed rotation of the light deflector. Also, a semiconductorlaser array having a plurality of light-emitting points enclosed in onepackage is used as the light source in the case of high-speed outputmachine is configured. In such a case, the holding member holding thesemiconductor laser array can also be used in common in a case where thelight source has a single light emitting point.

[0096] On the other hand, in view of compactness of the machine, thereis a method in which the coupling lens 2 and line-image imaging opticalsystem 4 are integrated (into a single lens), and the holding member 16shown ion FIG. 6 is miniaturized. Also in this case, it is preferablethat the beam emitted from the thus-integrated coupling lens 2 is anapproximately parallel beam, as mentioned above.

[0097] With reference to FIG. 3, a specific method of contriving aspecific amount to shift the light-source part 15 and holding member 16will now be described. In FIG. 3, when the cover member 14 is used, thelight path of the beam ‘a’ from the light-source part 15 is shifted by adistance Δ1 by the transparent cover member 14. The beam is thenreflected by the deflection reflective surface 5 a, and, then, the lightpath of the beam is again shifted by a distance A2 by the transparentcover member 14. The total thereof, that is,

Δ=Δ1+Δ2

[0098] is the amount to shift the light-source part 15 in a directionperpendicular to the optical axis of the light-source part 15. In FIG.3, it is assumed that directions parallel to the optical axis of thescanning and imaging system is an x-axis, and directions perpendicularthereto is a y-axis. Further, it is assumed that the beam ‘c’ emittedfrom the cover member 14 goes along a direction parallel to the x-axis.

[0099]FIG. 7 shows FIG. 3 in more detail. In FIG. 7,

[0100] φ denotes an angle of the cover member 14 with respect to they-axis;

[0101] θ denotes an angle between the beam incident on the deflectionreflective surface 5 a and the beam reflected thereby;

[0102] θ—φ denotes an angle between the normal of the cover member 14and the incident beam ‘a’;

[0103] α denotes an angle between the beam refracted by the cover member14 and the normal thereof;

[0104] n denotes a refractive index of the cover member 14;

[0105] S denotes a length of light path of the beam passing through thecover member 14; and

[0106] t denotes a thickness of the cover member 14.

[0107] Then, n ⋅ sin   α = sin (θ − φ) S ⋅ sin   α = t$\begin{matrix}{{\Delta 1} = \quad {S \cdot {\sin \left( {\theta - \varphi - \alpha} \right)}}} \\{= \quad {\left( {{t/\cos}\quad \alpha} \right) \cdot {\sin \left( {\theta - \varphi - \alpha} \right)}}}\end{matrix}$

[0108] Similarly, with regard to the beam reflected by the deflectionreflective surface 5 a,

[0109] γ denotes an angle between the beam refracted by the cover member14 and the normal thereof; and

[0110] u denotes a length of light path of the beam passing through thecover member 14.

[0111] Then, n ⋅ sin   γ = sin   φ u ⋅ cos   γ = t $\begin{matrix}{{\Delta 2} = {u \cdot {\sin \left( {\varphi - \gamma} \right)}}} \\{= {\left( {{t/\cos}\quad \gamma} \right) \cdot {\sin \left( {\varphi - \gamma} \right)}}}\end{matrix}$

[0112] Accordingly, $\begin{matrix}{\Delta = \quad {{\Delta 1} + {\Delta 2}}} \\{= \quad {t \cdot \left\{ {{\left( {{1/\cos}\quad \alpha} \right) \cdot {\sin \left( {\theta - \varphi - \alpha} \right)}} +} \right.}} \\\left. \quad {\left( {{1/\cos}\quad \gamma} \right) \cdot {\sin \left( {\varphi - \gamma} \right)}} \right\}\end{matrix}$

[0113] In the above-described example, by shifting the optical axis ofthe light-source part, whether or not the transparent cover memberhaving the soundproof and dustproof functions is used is dealt with.However, as an another method, it is possible to deal therewith bychanging the angle of the beam coming from the light-source part towardthe light deflector 5, as shown in FIG. 8. In FIG. 8, the beam from thelight-source part toward the light deflector 5 is inclined by an angle ηwhen the cover member 14 is not used, in comparison to the case wherethe cover member 14 is used.

[0114] Actually, the angle θ′ between the beam incident on thedeflection reflective surface 5 a of the light deflector 5 and-the beamreflected thereby is smaller by the angle η than the angle θ between thebeam incident on the deflection reflective surface 5 a of the lightdeflector 5 and the beam reflected thereby in the case where the covermember 14 is used. That is, should be such that

θ′=θ−η

[0115] Accordingly, in order to cause the beam to be reflected in thedirection ‘c’ parallel to the x-axis, and angle ε′ between the normal ofthe deflection reflective surface 5 a and the x-axis when the covermember is not used should be such that

ε′=ε−(η/2)

[0116] where ε denotes an angle between the normal of the deflectionreflective surface 5 a and the x-axis in the case where the cover member14 is used.

[0117] Thus, it is possible to deal with whether or not the cover member14 is used, by changing the direction in which the beam is emitted fromthe light-source part without translating the light-source part.

[0118] Further, the influence by the so-called floating due to the covermember 14 is the same between the case where the light-source part istranslated and the case where the direction of the beam emitted from thelight-source part is changed, according to whether or not the covermember 14 is used. Accordingly, it is possible that various designrequirements such as the position of the line-image imaging opticalsystem 4, parallelity of the beam emitted from the light-source part andso forth are the same as those in the case where the light-source partis translated. Further, a plurality of holding and fixing datums of thelight-source part are provided so as to deal with the case where thecover member 14 is used and the case where the cover member 14 is notused, for the purpose of appropriately changing the direction of thebeam incident on the light deflector 5 as mentioned above.

[0119] Further, it is also possible that the line-image imaging opticalsystem is separate from the light-source part, and, the position of theline-image imaging optical system along the directions of the opticalaxis thereof is shifted, thereby whether or not the cover member 14 isused is dealt with. In this case, the beam emitted from the couplinglens does not need to be an approximately parallel beam, and, may be aconvergent beam or a convergent beam. In such a case, the position ofthe light-source part along the directions of the optical axis thereofshould be changed so as to correct the influence of the so-calledfloating occurring due to disposition of the cover member.

[0120]FIG. 9 is a general plan view showing an optical scanning devicein a first embodiment of a second aspect of the present invention. Asshown in FIG. 9, the optical scanning device includes a light-sourceunit 101, a first imaging optical system 102, a deflector (polygonmirror) 103, a second imaging optical system 104 and a transparentmember 105 of an approximately parallel plate.

[0121] The light-source unit 101 emits a beam. The first imaging opticalsystem 102 causes the beam emitted from the light-source unit 101 toimage at a predetermined position. The deflector 103 is rotated in apredetermined direction at a fixed velocity, and, also, receives thebeam from the first imaging optical system 102 and scans a surface to bescanned 106 thereby.

[0122] The light-source unit 101 includes a light source 101 a emittingthe beam, a coupling lens 101 b condensing the beam emitted by the lightsource 101 a and an aperture 101 c reducing the beam from the couplinglens 101 b in diameter. The transparent member 105 is disposeddetachably between the first imaging optical system 102 and deflector103 and between the deflector 103 and second imaging optical system 104.The transparent member 105 is used for the purpose of soundproof anddustproof. The light-source unit 101, first imaging optical system 102,deflector 103, second imaging optical system 104 and transparent member105 are mounted in a box housing 107.

[0123]FIG. 10 shows a difference in light path of the beam between acase where the optical scanning device has the transparent member 105and the case where the optical scanning device does not have thetransparent member 105. In FIG. 10, a broken line represents the axis ofthe beam in the case where the optical scanning device has thetransparent member 105, while a solid line represents the axis of thebeam in the case where the optical scanning device does not have thetransparent member 105. As shown in FIG. 10, it is clear that adeviation of axis of the beam (optical-axis deviation) occurs due towhether or not the transparent member 105 is used.

[0124]FIG. 11 shows a floating amount (C1, C2′) of an optical imagealong directions of the axis of the beam and a deviation amount (C1, C2)of the axis of the beam in the case where the transparent member 105 isused in the optical scanning device. As shown in FIG. 11, assuming thatb denotes a length of light path in the transparent member 105 of thebeam coming from the first imaging optical system 102 and u denotes anincident angle onto the transparent member 105, the floating amount C1′of the optical image along the directions of the axis of the beam andthe deviation amount C1′ of the axis of the beam are expressed asfollows:

C1=b cos u

C1=b sin u

[0125] Further, assuming that b′ denotes a length of light path in thetransparent member 105 of the beam coming from the deflector 103 and u′denotes an incident angle onto the transparent member 105, the floatingamount C2′ of the optical image along the directions of the axis of thebeam and the deviation amount C2 of the axis of the beam are expressedas follows:

C2′=b cos u′

C2=b′ sin u′

[0126] The optical scanning device in the first embodiment of the secondaspect of the present invention prevents these deviations of the axis ofthe beam.

[0127]FIGS. 12A and 12B show an essential part of the above-mentionedoptical scanning device in the first embodiment of the second aspect ofthe present invention. As shown in FIGS. 12A and 12B, the second imagingoptical system 104 has a projection 108 for positioning the system 104along main scanning directions (directions perpendicular to the opticalaxis of the second scanning and imaging optical system 104). In the boxhousing 107, two receiving parts 109 and 110 are formed with apredetermined interval therebetween along the directions perpendicularto the optical axis of the second scanning and imaging optical system104. The projection 108 of the second scanning and imaging opticalsystem 104 is disposed between these two receiving parts 109 and 110.

[0128] By causing the projection 108 of the second scanning and imagingoptical system 104 to come into contact with either one of the tworeceiving parts 109 and 110, the positioning of the second scanning andimaging optical system 104 along the main scanning directions isperformed. That is, when the optical scanning device does not employ thetransparent member 105, the axis of the beam is as indicated by thesolid line shown in FIG. 10. Therefore, as shown in FIG. 12B, thepositioning of the second scanning and imaging optical system 104 isperformed in a condition in which the projection 108 is in contact withthe receiving part 109. Thereby, the second scanning and imaging opticalsystem 104 is disposed as indicated by a solid line shown in FIG. 10.However, when the optical scanning device employs the transparent member105, the axis of the beam is as indicated by the broken line shown inFIG. 10. Therefore, as shown in FIG. 12A, the positioning of the secondscanning and imaging optical system 104 is performed in a condition inwhich the projection 108 is in contact with the receiving part 110.Thereby, the second scanning and imaging optical system 104 is disposedas indicated by a broken line shown in FIG. 10. Thus, the amount ofdeviation in beam axis occurring due to whether or not the transparentmember 105 is employed in the optical scanning device is canceled as aresult of the second scanning and imaging optical system 104 beingpositioned as a result of the projection 108 thereof being caused to bein contact with a respective one of the two receiving parts 109 and 110.

[0129] With reference to FIGS. 9, 13A and 13B, a second embodiment ofthe second aspect of the present invention will now be described. FIGS.13A and 13B show an essential part of the optical scanning device in thesecond embodiment of the second aspect of the present invention. InFIGS. 13A and 13B, the same reference numerals are given toparts/components the same as those of the first embodiment of the secondaspect of the present invention shown in FIGS. 12A and 12B. As shown inFIGS. 13A and 13B, the second imaging optical system 104 has ribs 111 atboth ends thereof. The ribs 111 are used for positioning the secondscanning and imaging optical system 104 along the directions of theoptical axis of the optical system 104. In the box housing 107, twopairs of rib-receiving parts 112 and 113 are formed with a predeterminedinterval therebetween along the directions of the optical axis of thesecond scanning and imaging optical system 104. Each rib 111 of thesecond scanning and imaging optical system 104 is disposed between arespective pair of the two pairs of rib-receiving parts 112 and 113.

[0130] By causing each rib 111 of the second scanning and imagingoptical system 104 to come into contact with either one of a respectivepair of the two pairs of rib-receiving parts 112 and 113, thepositioning of the second scanning and imaging optical system 104 isperformed. That is, when the optical scanning device does not employ thetransparent member 105, the axis of the beam is as indicated by thebroken line shown in FIG. 11. Therefore, as shown in FIG. 13B, thepositioning of the second scanning and imaging optical system 104 isperformed in a condition in which each rib 111 is in contact with therib-receiving part 113 of the respective pair. However, when the opticalscanning device employs the transparent member 105, the axis of the beamis as indicated by the solid line shown in FIG. 11. Therefore, as shownin FIG. 13A, the positioning of the second scanning and imaging opticalsystem 104 is performed in a condition in which each rib 111 is incontact with the rib-receiving part 112 of the respective pair. Thus,the amount of floating of optical image along the directions of beamaxis occurring due to whether or not the transparent member 105 isemployed in the optical scanning device is canceled as a result of thesecond scanning and imaging optical system 104 being positioned as aresult of each rib 111 thereof being caused to be in contact with anappropriate one of the rib-receiving parts 112 and 113 of the respectivepair.

[0131]FIGS. 14A and 14B show an essential part of an optical scanningdevice in a third embodiment of the second aspect of the presentinvention. In FIGS. 14A and 14B, the same reference numerals are givento parts/components the same as those of the first embodiment of thesecond aspect of the present invention shown in FIGS. 12A and 12B andsecond embodiment of the second aspect of the present invention shown inFIGS. 13A and 13B.

[0132] The third embodiment of the second aspect of the presentinvention is a combination of the above-described first and secondembodiments of the second aspect of the present invention. As shown inFIGS. 14A and 14B, the second imaging optical system 104 has aprojection 108 for positioning the optical system 104 along the mainscanning directions (directions perpendicular to the optical axis of thesecond scanning and imaging optical system 104). In the box housing 107,two receiving parts 109 and 110 are formed with a predetermined intervaltherebetween along the directions perpendicular to the optical axis ofthe second scanning and imaging optical system 104. The projection 108of the second scanning and imaging optical system 104 is disposedbetween these two receiving parts 109 and 110. Positioning of the secondimaging optical system 104 along the main scanning directions isperformed as a result of the projection 108 thereof being caused to comeinto contact with either one of the two receiving parts 109 and 110.

[0133] The amount of deviation of beam axis along the main scanningdirections occurring due to whether or not the transparent member 105 isemployed in the optical scanning device is canceled as a result of thesecond scanning and imaging optical system 104 being positioned as aresult of the projection 108 thereof being caused to be in contact witha respective one of the two receiving parts 109 and 110.

[0134] Further, the second imaging optical system 104 has ribs 111 atboth ends thereof. The ribs 111 are used for positioning the secondscanning and imaging optical system 104 along the directions of theoptical axis of the optical system 104. In the box housing 107, twopairs of rib-receiving parts 112 and 113 are formed with a predeterminedinterval therebetween along the directions of the optical axis of thesecond scanning and imaging optical system 104. Each rib 111 of thesecond scanning and imaging optical system 104 is disposed between arespective pair of the two pairs of rib-receiving parts 112 and 113.

[0135] The amount of floating of optical image along the directions ofbeam axis occurring due to whether or not the transparent member 105 isemployed in the optical scanning device is canceled as a result of thesecond scanning and imaging optical system 104 being positioned alongthe directions of the optical axis thereof as a result of each rib 111thereof being caused to be in contact with an appropriate one of therib-receiving parts 112 and 113 of the respective pair.

[0136] With reference to FIG. 15, an image forming apparatus in oneembodiment of the present invention will now be described.

[0137] The image forming apparatus shown in FIG. 15 is a laser printer,for example.

[0138] This laser printer 1100 has a cylindrical photoconductivephotosensitive body acting as a photosensitive medium 1111. In theperiphery of the photosensitive medium 1111, a charging roller 1112acting as a charging unit, a developing device 1113, a transfer roller1114, and a cleaning device 1115 are disposed. It is also possible touse a well-known corona charger as the charging unit.

[0139] Further, an optical scanning device 1117 using a laser beam LB isprovided, and performs exposure through optical writing between thecharging roller 1112 and developing device 1113.

[0140] As shown in FIG. 15, a fixing device 1116, a cassette 1118, apair of registration rollers 1119, a paper feeding roller 1120, aconveying path 1121, a pair of paper ejecting rollers 1122, and a tray1123 are also provided. Transfer paper P is used as a sheet-typerecording medium.

[0141] When image formation is performed, the photosensitive medium 1111is rotated clockwise at a uniform velocity, the surface thereof ischarged uniformly by the charging roller 1112, and an electrostaticlatent image is formed on the surface (surface to be scanned) of thephotosensitive medium 1111 through exposure by optical writing with thelaser beam LB of the optical scanning device 1117. The thus-formedelectrostatic latent image is a so-called negative latent image havingan image part exposed thereby.

[0142] This electrostatic latent image is developed inversely by thedeveloping device 1113, and, thus, a toner image is formed on thephotosensitive medium 1111.

[0143] The cassette 1118 containing the transfer paper P is detachablefrom/to the body of the image forming apparatus 1100. In the state inwhich the cassette 1118 is loaded as shown in the figure, the top onesheet of the transfer paper P is fed by the paper feeding roller 1120.The thus-fed transfer paper P is nipped by the pair of registrationrollers 1119 at the top of the paper P. The pair of registration rollers1119 feed the transfer paper P to a transfer position of thephotosensitive medium 1111 at the time at which the toner image is movedto the transfer position. The fed transfer paper P is laid onto thetoner image at the transfer position, and, by the function of thetransfer roller 1114, the toner image is transferred to the transferpaper P electrostatically.

[0144] The transfer paper P thus having had the toner image transferredthereto is sent to the fixing device 1116, which fixes the toner imageonto the transfer paper P. Then, the transfer paper P passes through theconveying path 1121, and is ejected to the tray 1123 by the pair ofejecting rollers 1122. The surface of the photosensitive medium 1111 isthen cleaned by the cleaning device 1115, and, thus, remaining toner,paper powder and so forth are removed therefrom.

[0145] It is also possible to use an OHP sheet instead of theabove-mentioned transfer paper. A provision may be made such that thetransfer of the toner image is performed via an intermediate transfermedium such as an intermediate transfer belt or the like. By employingthe optical scanning device including the scanning and imaging lens suchas that in any of the first, second and third embodiments of the firstaspect of the present invention described above with reference to FIGS.1 through 8, and, the first, second and third embodiments of the secondaspect of the present invention described above with reference to FIGS.9 through 14B, as the optical scanning device 1117 of theabove-described image forming apparatus in the embodiment of the presentinvention shown in FIG. 15, it is possible to render satisfactory properimage formation.

[0146] The present invention is not limited to the above-describedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

[0147] The present application is based on Japanese priorityapplications Nos. 2000-180391 and 2000-111729, filed on Jun. 15, 2000and Apr. 13, 2000, respectively, the entire contents of which are herebyincorporated by reference.

What is claimed is:
 1. An optical scanning device comprising: a lightsource; a coupling lens coupling a beam emitted from said light source;a light deflector deflecting the beam from said coupling lens at auniform angular velocity; a line-image imaging optical system disposedbetween said coupling lens and light deflector, and causing the beam toimage a line image long along main scanning directions on or in thevicinity of a deflection reflective surface of said light deflector; ascanning and imaging optical system causing the beam deflected by saidlight deflector to image a beam spot on a medium to be scanned; and anoptical housing in which said light source, coupling lens, lightdeflector, line-image imaging optical system and scanning and imagingoptical system are disposed, and contained, and wherein a plurality ofholding and fixing datums for holding and fixing a light-source partcomprising said light source and coupling lens are provided in at leastone of said light-source part and optical housing.
 2. The device asclaimed in claim 1 , wherein: said light deflector is covered by acover; said cover has a window for the beam to be incident on and exitfrom said light deflector; and a transparent cover member can be mountedon said window, and wherein said holding and fixing datums aredetermined so that, by selectably using said holding and fixing datums,the beam deflected by said light deflector passes through said scanningand imaging optical system approximately at the same position whether ornot said transparent cover member is mounted.
 3. The device as claimedin claim 1 , wherein said light-source part and line-image imagingoptical system are disposed on a common member.
 4. The device as claimedin claim 1 , wherein said coupling lens and line-image imaging opticalsystem are formed integrally.
 5. The device as claimed in claim 1 ,wherein said light-source part comprises a plurality of light-emittingsources.
 6. The device as claimed in claim 3 , wherein the beam emittedfrom said light-source part comprises an approximately parallel beam. 7.The device as claimed in claim 4 , wherein the beam emitted from saidlight-source part comprises an approximately parallel beam.
 8. Anoptical scanning device comprising: a light-source unit emitting a beam;a first imaging optical system causing the beam emitted by saidlight-source unit to image at a predetermined position; a deflectorreceiving the beam from said first imaging optical system and performingscanning with the beam; and a second imaging optical system causing thebeam from said deflector to image a beam spot on a surface to bescanned, and wherein: said light-source unit, first imaging opticalsystem, deflector and second imaging optical system are mounted in a boxhousing; a transparent member of an approximately parallel plate isdisposed detachably so as to be located between said first imagingoptical system and deflector and between said deflector and secondimaging optical system; and a mounting position of said second imagingoptical system can be changed according to whether or not saidtransparent member is provided.
 9. The device as claimed in claim 8 ,wherein the mounting position of said second imaging optical systemalong main scanning directions can be changed according to whether ornot said transparent member is used.
 10. The device as claimed in claim8 , wherein the mounting position of said second imaging optical systemalong directions of an optical axis thereof can be changed according towhether or not said transparent member is used.
 11. The device asclaimed in claim 8 , wherein the mounting position of said secondimaging optical system along main scanning directions and directions ofan optical axis thereof can be changed according to whether or not saidtransparent member is used.
 12. An optical scanning device comprising:light emitting means for emitting a beam; coupling means for couplingthe beam emitted by said light emitting means; light deflecting meansfor deflecting an incident beam at a uniform angular velocity;line-image imaging means for causing the beam coupled by said couplingmeans to image a line image long along main scanning directions on or inthe vicinity of a deflection reflective surface of said light deflectingmeans; scanning and imaging means for causing the beam deflected by saidlight deflecting means to image a beam spot on a medium to be scanned;and an optical housing in which said light emitting means, couplingmeans, light deflecting means, line-image imaging means and scanning andimaging means are disposed, and contained, and wherein a plurality ofholding and fixing datums for holding and fixing a light-source partcomprising said light emitting means and coupling means are provided inat least one of said light-source part and optical housing.
 13. Anoptical scanning device comprising: light-source means for emitting abeam; first imaging means for causing the beam emitted by saidlight-source means to image at a predetermined position; deflectingmeans for receiving the beam from said first imaging means andperforming scanning with the beam; and second imaging means for causingthe beam from said deflecting means to image a beam spot on a surface tobe scanned, and wherein: said light-source means, first imaging means,deflecting means and second imaging means are mounted in a box housing;a transparent member of an approximately parallel plate is disposeddetachably so as to be located between said first imaging means anddeflecting means and between said deflecting means and second imagingmeans; and a mounting position of said second imaging means can bechanged according to whether or not said transparent member is provided.14. An image forming apparatus comprising: an optical scanning devicescanning a surface of a photosensitive body with a beam so as to form alatent image on said photosensitive body; said photosensitive body; adeveloping device developing the latent image so as to form a visibleimage; a transferring device transferring the visible image to a sheetrecording medium; and a fixing device fixing the visible image onto thesheet recording medium, and wherein said optical scanning devicecomprises: a light source; a coupling lens coupling a beam emitted fromsaid light source; a light deflector deflecting the beam from saidcoupling lens at a uniform angular velocity; a line-image imagingoptical system disposed between said coupling lens and light deflector,and causing the beam to image a line image long along main scanningdirections on or in the vicinity of a deflection reflective surface ofsaid light deflector; a scanning and imaging optical system causing thebeam deflected by said light deflector to image a beam spot on a mediumto be scanned; and an optical housing in which said light source,coupling lens, light deflector, line-image imaging optical system andscanning and imaging optical system are disposed, and contained, andwherein a plurality of holding and fixing datums for holding and fixinga light-source part comprising said light source and coupling lens areprovided in at least one of said light-source part and optical housing.15. An image forming apparatus comprising: an optical scanning devicescanning a surface of a photosensitive body with a beam so as to form alatent image on said photosensitive body; said photosensitive body; adeveloping device developing the latent image so as to form a visibleimage; a transferring device transferring the visible image to a sheetrecording medium; and a fixing device fixing the visible image onto thesheet recording medium, and wherein said optical scanning devicecomprises: a light-source unit emitting a beam; a first imaging opticalsystem causing the beam emitted by said light-source unit to image at apredetermined position; a deflector receiving the beam from said firstimaging optical system and performing scanning with the beam; and asecond imaging optical system causing the beam from said deflector toimage a beam spot on a surface to be scanned, and wherein: saidlight-source unit, first imaging optical system, deflector and secondimaging optical system are mounted in a box housing; a transparentmember of an approximately parallel plate is disposed detachably so asto be located between said first imaging optical system and deflectorand between said deflector and second imaging optical system; and amounting position of said second imaging optical system can be changedaccording to whether or not said transparent member is used.